The invention relates to a disc brake for a utility vehicle having a brake caliper engaging over a brake disc, and at least one application device for applying the disc brake by way of a displaceably guided bridge, wherein the bridge has at least one threaded borehole, into which an actuating spindle passing through a closure plate connected to the brake caliper and provided with an external thread is screwed. The spindle bears a pressure piece, which can be rotated relative thereto, by which pressure piece a brake pad can be pressed against the brake disc.
A disc brake of this kind is disclosed in DE 94 22 342 U1. This disc brake comprises a brake lever, which acts on the bridge during a braking process, in which at least one actuating spindle is mounted and able to rotate by means of a threaded pair. The spindle has a pressure piece, which is pressed against a brake disc when the brake is activated by displacement of the bridge.
In order to cancel out a wear-related change in a predetermined clearance, i.e., the distance between the brake pad and the brake disc, a readjusting device is provided, with which the actuating spindle is adjusted by rotation in the direction of the brake disc. For this, the actuating spindle is provided with an external thread, which engages with a corresponding threaded borehole of the bridge.
A receiving space of the brake caliper, in which the bridge and the brake lever are positioned, is closed on the outside, i.e., toward the brake disc, by a closure plate, through which the actuating spindle passes.
In order to seal off this passageway, there is provided a bellows, which is held on the one hand against the closure plate and on the other hand against the pressure piece. This usually consists of a highly elastic material, such as a silicone rubber, so that it can cover the actuating spindle over the entire adjustment range. For the resetting of the bridge after a braking event, a compression spring is arranged between the closure plate and the bridge.
Problems occur in terms of loading capacity, i.e., the service life of the bellows, since the relatively high temperatures during a braking process act on the bellows, and so the bellows must be replaced as the part wears.
However, due to the narrow space conditions, this can only be done with considerable labor, having a definite negative influence on the servicing costs of the disc brake.
Apart from the time expenditure, in order to replace the bellows, and also to replace the brake pad, the actuating spindles are rotated back via the readjusting device, wherein in order to protect it during the backward and forward movement a breakaway adapter is used, which breaks upon passing a certain torque and thereby protects an adjuster of the readjusting device against excessive loading. Furthermore, a release protection of the readjusting device is needed, or else the actuating spindle will be axially strained against the adjuster, with the result that a larger torque is needed for the releasing than the breakaway adapter can transmit.
The problem which the invention proposes to solve is to modify a disc brake of this kind so that it is more simple and economical to produce and install, and the replacement of worn parts is made easier and avoids damaging of the functional parts involved in the replacement.
This problem is solved by a disc brake in accordance with embodiments of the invention.
The new disc brake is characterized, first of all, in that it is much easier to produce than heretofore. In particular, the release protection of the readjusting device mentioned in the prior art can be omitted, since a reversing protection is created by a securing ring provided according to the invention.
In this way, a reversing stop is created for the actuating spindle, by which the aforementioned problem of the axial strain of the actuating spindle is prevented.
The securing ring provided for this according to the invention, which is held on the bridge so as to be secured axially and against rotation, then engages with a form fit in the actuating spindle when the latter has reached an end position screwed into the bridge counter to the application direction, so that the securing ring prevents the actuating spindle from being rotated further back into a position in which said axial straining of the actuating spindle would be possible.
Because this is effectively prevented, the long-term functionality of the breakaway adapter is also assured, especially since the driving force of the breakaway adapter is sufficient during the subsequent forward rotation of the actuating spindle. Obviously, this improves the functional reliability, and also the repair work, which may result from the malfunctioning of the actuating spindle in the prior art, is no longer necessary.
The form fit provided by the invention between the securing ring and the actuating spindle in its thread-free end region can be accomplished in that the securing ring has form fit elements which engage with the actuating spindle in the mentioned position, so that its rotation is blocked.
Corresponding to the form fit elements of the securing ring, the actuating spindle has, at least in the thread-free end region, axial grooves which engage with the form fit elements of the securing ring when the end position of the actuating spindle is reached.
In order to enable a free turning of the actuating spindle with respect to the stationary securing ring outside of the mentioned end position, the thread-free end region of the actuating spindle which receives the axial grooves is increasingly larger in diameter than the threaded region. For this purpose, the end region may be configured as an encircling fillet, which passes into a head against which the pressure piece is supported. That is, the axial grooves effectively form a curved indentation of this fillet.
For the holding of the securing ring stationary in relation to the bridge, i.e., for a rotational and axial securing, according to another aspect of the invention the securing ring is held against the bridge by a preferably frictionally secured holding ring. For this, the holding ring has an encircling collar, extending axially to the actuating spindle, whose clear diameter is chosen such that a press fit with a corresponding shoulder of the bridge results.
Radially inward, i.e., at an angle relative to the actuating spindle, a contact leg is formed on the collar, forming an axial securement for the securing ring, which is furthermore inserted in a groove produced concentric to the shoulder of the bridge, the clear diameter of the passageway for the actuating spindle that is bounded by the contact leg being larger than the diameter, especially the thread diameter, of the actuating spindle, so that it can rotate freely.
For the rotational locking of the securing ring, the holding ring has at least one cut-out in the region of the radial contact leg, through which passes a somewhat axially angled tab of the securing ring, lying against the boundary walls of the cut-out in the rotating direction of the actuating spindle.
The tab, preferably several of them being provided evenly distributed about the circumference, is moreover shaped such that it lies against the actuating spindle for radial bracing of the securing ring. Outside of the tabs, the clear diameter of the securing ring is likewise larger than the diameter of the actuating spindle, especially in the thread region.
For the reversing protection of the actuating spindle, the securing ring has, as a form fit element, at least one tongue protruding radially inward, which then engages in the rotating direction by form fit with the axial groove of the actuating spindle when its curved portion, during an axial adjusting movement of the actuating spindle, assumes a position in which the tongue protrudes into the axial groove.
Advantageously, several axial grooves are provided in the actuating spindle, arranged parallel to and at a distance from each other, being situated at the same angular distance relative to each other, as are the tongues engaging with them in the aforesaid position of the actuating spindle.
Other design solutions are also contemplated for the immovable holding of the securing ring relative to the bridge. For example, the securing ring may be held by press fit against the bridge, the frictional forces holding the securing ring being larger than the forces applied for the backward rotation of the actuating spindle. This equally holds for the frictional forces by which the holding ring is held against the bridge.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.